The present invention relates to a new and distinct cultivar of Potentilla, commonly known as Bush Cinquefoil, or Shrubby Potentilla, which is grown as a dwarf summer-flowering shrub for use in the garden and landscape. The new cultivar is known botanically as Potentilla fruticosa, and will be referred to hereinafter by the cultivar name ‘Summer Dawn’. ‘Summer Dawn’ arose from a breeding program carried out by the inventor at the inventor's nursery on the Island of Orkney in Scotland, United Kingdom, which the inventor commenced in 1976.
Shrubby Potentillas are especially well-adapted to the harsh weather conditions of Orkney which experiences long, dull and wet winters, with salt-laden winds and frequent severe gales. Summers are short and cool, and the prevailing soil type is heavy boulder clay. Although potentillas suffer die-back in these conditions, re-growth occurs quickly and flowering occurs and persists during the summer and early autumn months.
Initially, the inventor gathered together approximately sixty named cultivars of Potentilla, and planted them in the open ground with the intention of facilitating open pollination. Seed was harvested each autumn and seedlings raised the following spring. As the inventor observed the flowering and plant habit of each new seedling, it was either discarded or re-planted in association with similar selections in order to encourage open pollination within each color group. The initial aim of the breeding program was to produce robust white-flowered forms. More recently the inventor has been interested in producing a collection of new Potentilla varieties with novel flower colors and improved plant habit leading to better garden and landscape performance.
‘Summer Dawn’ was identified and selected in 1985 for its useful combination of attractive pale yellow flowers which are large in comparison with other cultivars of similar color known to the inventor, a long flowering period, and a compact habit without pruning, even after 20 years of observation in the ground.
The male and female parents of ‘Summer Dawn’ were unnamed, unreleased seedlings which the inventor had raised from previous open pollinations going back to the inventor's original acquisition of named cultivars.
The cultivar of potentilla which is considered to be closest in flower color and plant habit to ‘Summer Dawn’ is the variety ‘Primrose Beauty’ (unpatented). Whereas ‘Primrose Beauty’ achieves a height of 1.3 meters to 1.7 meters, and a spread of 2 meters, ‘Summer Dawn’ has remained compact, not exceeding 1 meter in height and spread, even after 20 years. The diameter of the flowers of ‘Primrose Beauty’ is 25 mm, whereas the flowers of ‘Summer Dawn’ are 35 mm-50 mm in diameter.
‘Summer Dawn’ was first asexually propagated by the inventor in Orkney, Scotland, United Kingdom in summer 1985, by taking softwood cuttings. The plants resulting from this first and from all subsequent generations have grown and flowered uniformly and identically with the inventor's initial selection. The inventor has determined that the new variety ‘Summer Dawn’ is stable and reproduces true to type in successive generations of asexual propagation.